title: Lipopolysaccharides elicit an oxidative burst as a component of the innate immune system in the seagrass Thalassia testudinum.
abstract: This study represents the first report characterizing the biological effects of a lipopolysaccharide (LPS) immune modulator on a marine vascular plant. LPS was shown to serve as a strong elicitor of the early defense response in the subtropical seagrass Thalassia testudinum Banks ex König and was capable of inducing an oxidative burst identified at the single cell level. The formation of reactive oxygen species (ROS), detected by a redox-sensitive fluorescent probe and luminol-based chemiluminescence, included a diphenyleneiodonium sensitive response, suggesting the involvement of an NADPH oxidase. A 900 bp cDNA fragment coding for this enzyme was sequenced and found to encode a NAD binding pocket domain with extensive homology to the Arabidopsis thaliana rbohF (respiratory burst oxidase homolog) gene. The triggered release of ROS occurred at 20 min post-elicitation and was dose-dependent, requiring a minimal threshold of 50 μg/mL LPS. Pharmacological dissection of the early events preceding ROS emission indicated that the signal transduction chain of events involved extracellular alkalinization, G-proteins, phospholipase A2, as well as K(+), Ca(2+), and anion channels. Despite exclusively thriving in a marine environment, seagrasses contain ROS-generating machinery and signal transduction components that appear to be evolutionarily conserved with the well-characterized defense response systems found in terrestrial plants.
authors.affiliation: Department of Biology, University of North Florida, 1 UNF Drive, Jacksonville, FL 32224, USA.
authors.forename: Kyle
authors.initials: K
authors.lastname: Loucks
authors.forename: David
authors.initials: D
authors.lastname: Waddell
authors.forename: Cliff
authors.initials: C
authors.lastname: Ross
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D001483:Base Sequence; D018076:DNA, Complementary; D019143:Evolution, Molecular; D019204:GTP-Binding Proteins / Q000378:metabolism; D031321:Hydrocharitaceae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D054467:Phospholipases A2 / Q000378:metabolism; D010935:Plant Diseases / Q000139:chemically induced*; D057865:Plant Immunity / Q000187:drug effects* / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*; D016897:Respiratory Burst / Q000187:drug effects* / Q000235:genetics; D017385:Sequence Homology; D015398:Signal Transduction; D013312:Stress, Physiological / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D007473:Ion Channels; D008070:Lipopolysaccharides; D017382:Reactive Oxygen Species; C568857:AT5G47910 protein, Arabidopsis; D019255:NADPH Oxidases; D054467:Phospholipases A2; D019204:GTP-Binding Proteins
keywords: 2′,7′-dichlorodihydrofluoresceindiacetate; DPI; Elicitation; H(2)DCF-DA; H(2)O(2); Hydrogen peroxide; LPS; NADPH; Oxidative burst; PAMP; Pathogen defense; RBOH; ROS; SAR; SSA; Seagrass; Signaling pathways; diphenyleneiodonium; hydrogen peroxide; lipopolysaccharide; nicotinamide adenine dinucleotide phosphate; pathogen-associated molecular pattern; reactive oxygen species; respiratory burst oxidase homolog; serum-seawater agar; systemic acquired resistance